There is a continuous development of new generations of mobile communications technologies to cope with increasing requirements of higher data rates, improved efficiency and lower costs. High Speed Downlink Packet Access (HSDPA) and High Speed Uplink Packet Access (HSUPA), together referred to as High Speed Packet Access (HSPA), are mobile communication protocols that were developed to cope with higher data rates than original Wideband Code Division Multiple Access (WCDMA) protocols were capable of. The 3rd Generation Partnership Project (3GPP) is a standards-developing organization that is continuing its work of evolving HSPA and creating new standards that allow for even higher data rates and improved functionality.
In a radio access network implementing HSPA, a user equipment (UE) is wirelessly connected to a radio base station (RBS) commonly referred to as a NodeB (NB). A radio base station is a general term for a radio network node capable of transmitting radio signals to a user equipment (UE) and receiving signals transmitted by a user equipment (UE).
Dual-Carrier High-Speed Downlink Packet Access (DC-HSDPA, also known as Dual-Cell HSDPA) was introduced within the 3GPP release 8. DC-HSDPA enables reception of data from two cells simultaneously, where the data is transmitted on two adjacent carriers from the same base station and sector to individual user equipments (UEs) or terminals. The concept of DC-HSDPA is in 3GPP release 10 extended to 4 downlink carrier frequencies known as 4-carrier-HSDPA (4C-HSDPA). With 4-carrier HSDPA the NodeB can schedule downlink transmission to one UE on up to four downlink carriers simultaneously and the UE can use up to two adjacent uplink carriers.
To complement DC-HSDPA, in 3GPP release 9, Dual-Carrier High-Speed Uplink Packet Access (DC-HSUPA) was also introduced. DC-HSUPA enables an individual terminal to transmit data on two adjacent carrier frequencies simultaneously to the radio access network. DC-HSUPA according to 3GPP release 9 is in essence an aggregation of legacy single-carrier HSUPA according to 3GPP release 8.
In multi-cell HSPA/multi-carrier HSPA (MC-HSPA), carriers that can be dynamically activated/deactivated are referred to as secondary carriers. A secondary carrier may be secondary downlink carrier or a secondary uplink carrier. The uplink and downlink carriers that cannot be deactivated are referred to as primary or anchor carriers. In 3GPP specifications a secondary downlink carrier is also referred to as a secondary serving HS-DSCH (High-Speed Downlink Shared Channel) cell and a secondary uplink carrier is also referred to as a secondary uplink frequency.
One of the important features in MC-HSPA systems is the serving NodeB's ability to dynamically determine which of the downlink carriers that a certain UE needs to listen to and which uplink carriers that a UE should transmit physical control channels and potential payload data on. An obvious reason for activating a secondary uplink or downlink carrier for a certain UE is to increase the instantaneous data rate. The additional spectrum bandwidth associated with multi-carrier operation does not increase “spectral efficiency”, i.e. the maximum achievable throughput per cell per Hz [bps/cell/Hz], but the experienced user data rates are increased significantly. In particular, for bursty packet data traffic at low and moderate load, the data rate is proportional to the number of carriers exploited. Moreover, power inefficient higher order modulation schemes can be avoided. This is especially important in the uplink. Furthermore, the practical as well as theoretical peak data rates of the system are naturally increased.
Handover and radio access bearer admission control is presumed to be conducted in a Radio Network Controller (RNC) based on measurements of e.g. path loss on a primary carrier. Notice though, that in case of a distributed radio access network (RAN) architecture where Node-B and RNC functionality, as defined in 3GPP specifications, is collocated in a base station, the base station would naturally handle also these functionalities. In a DC-HSUPA capable Node-B, the secondary carrier is assumed to be configured by the RNC for a given DC-HSUPA capable UE and then scheduled and activated by Node-B whenever feasible and useful. The decision whether to activate a secondary carrier may for example be driven by an objective to maximize the supported traffic volumes or the aggregate system throughput, subject to fairness criteria and quality of service constraints, such as minimum bit rate or maximum latency requirements. As mentioned above, a primary carrier, on the other hand, may not be temporarily deactivated by the Node-B. To deactivate a certain primary carrier for a connection, the connection is either released, or an inter-frequency handover is performed in which case another carrier will become the primary carrier.
For each user connected in DC-HSUPA mode, the serving Node-B hence controls whether or not a secondary carrier is activated, and a separate grant is selected for each activated carrier.
Furthermore, if a secondary carrier is activated by the Node-B, it is assumed that the Dedicated Physical Control Channel (DPCCH), which includes a sequence of pilot bits, is transmitted on that carrier, and the Node-B hence tries to detect this signal.
The minimum separation between the uplink and downlink frequencies may decrease as more downlink and uplink carriers are employed for an individual connection. For bands with small transmitter-receiver frequency separation, this may cause increased self-interference onto the downlink carriers that are closest to the uplink frequencies, thus degrading the performance on these carriers.